Inhibition of 141B decomposition

ABSTRACT

Inhibition of the formation of unsaturated carbon compounds during the heating of 141b involving the addition of various inhibitors such as butylene oxide and/or the use of a vessel made of a nickel alloy.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 07/983,919, filed on Dec.1, 1992, (now abandoned) which in turn is a continuation-in-part of thenapplication Ser. No. 07/869,225, filed on Apr. 14, 1992 (now abandoned).

FIELD OF THE INVENTION

The present invention relates to a method of inhibiting the formation ofunsaturated carbon compounds and other unwanted by-products formedduring the heating of 1,1-dichloro-1-fluoroethane ("141b"), especiallyas it relates to the separation of 141b from a liquid mixture containing1,1,1,2-tetrachloroethane ("130a") and, if present,1,1,1-trichloroethane ("140a") via distillation.

BACKGROUND OF THE INVENTION

The hydrochlorofluorocarbon 141b is a replacement fortrichlorofluoromethane ("11") as a foam blowing agent. As shown byBrooks et al. in U.S. Pat. No. 4,948,479 (the entire specification ofwhich is hereby incorporated by reference), however, the manufacture of141b from 140a and hydrogen fluoride ("HF") results in the formation ofvinylidene chloride ("1130a") and other unsaturated by-products andacids, principally HCl. Because of similar boiling points, 141b (b.p. 32C.) and 1130a (b.p. 31 C.) cannot be readily separated by distillation.Thus, Brooks et al. teach the use of a photochlorination step to convertthe 1130a in the 141b product stream to the higher boiling 130a (b.p.130.5 C.), then distillation of the photochlorinated liquid mixture toseparate the low boiling 141b from the higher boiling liquids such as130a (and possibly 140a unless it has been removed upstream). However,it is found that 1130a and acid (primarily HCl with lesser amounds ofHF) are reformed in the distillation column and distill overhead withthe 141b product. While the acid can be removed from the product byselective adsorption or reaction, such as by passing the acidic 141bthrough a bed of potassium hydroxide, it is undesirable since it is anadded step. Reformation of the 1130a is more difficult, however, becauseas noted above it has nearly the same boiling point as the desired 141bproduct. Thus, yet another post-treatment would be required to removethe 1130a unless its formation in the distillation column can beinhibited. The same problem is presented when 141b is formed by thereaction of 1130a and HF [as taught, for example, by Henne et al., JACS65, 1271 (1943)], resulting in a product stream containing 141b and1130a.

SUMMARY OF THE INVENTION

A method is provided for inhibiting the formation of unsaturated carboncompounds during the heating of 141b (alone or as a liquid mixturecontaining 130a or both 130a and 140a), which method comprisesconducting said heating (a) in the presence of an effective amount of aninhibitor selected from a dialkylhydroxylamine where the alkyl groupshave 1 to 4 carbons such as methyl, ethyl, propyl, or butyl [preferablydiethylhydroxylamine ("DEHA")]; an epoxide (or cyclic oxide) having 3 to6 or 10 to 30 carbons such as alpha-pinene oxide ("APO"), 1,2-hexadeceneoxide ("HO"), butylene oxide ("BO"), limonene monoxide, limonenedioxide, methyl epoxy soyate, propylene oxide, dicyclopentadiene dioxidealcohol, isoprene oxide, glycidyl isopropyl ether, 1,4-dioxane, or anepoxidized alpha olefin such as C₁₀ H₂₀ O, C₁₂ H₂₄ O, or C₁₆ H₃₂ O(preferably APO, HO, or BO); a free radical scavenger having at leasttwo double bonds and a boiling point greater than that of 141b such asalpha-methylstyrene ("AMS"), limonene or one of its optical isomers suchas d-limonene ("DL"), alloocimene, or isoprene (preferably AMS or DL); aphenol, the phenyl group of which can be unsubstituted or substituted atone or more of the ring positions with substituents separately selectedfrom alkyl (such as methyl, ethyl, isopropyl, butyl), alkoxy (such asmethoxy, ethoxy, propoxy, isopropoxy), nitro, halo (such as F, Cl, orBr), alkylamine salt (such as --N(CH₃)₃ +Cl⁻), acyl (--C(O)R where R isalkyl), acyloxy (--OC(O)R where R is alkyl), cyano, hydroxy, phenylwhich is unsubstituted or substituted as above, the alkyl portion ofsuch substituents generally being lower alkyl of 1 to 4 carbons, andwherein two adjacent positions of the phenyl group can have substituentswhich are joined to form a fused aromatic ring as in naphthol (preferredphenols being 2,6-di-t-butyl-4-methylphenol and 4-methoxyphenol); or a1,4-benzoquinone which can be unsubstituted or substituted at each ofthe aromatic ring positions with substituents separately selected fromthose listed for phenol (the preferred benzoquinone beingunsubstituted); or (b) in a vessel made of a nickel alloy.

This method is particularly applicable to separation of 141b from aliquid mixture containing 130a (and, optionally, 140a) in a distillationcolumn. If an inhibitor is used, it is added to the bottom (or"reboiler" section) of the column. If the column is made of a nickelalloy, use of an inhibitor is not necessary.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the invention it has now been found that thepresence of the aforementioned inhibitors inhibits the formation ofunsaturated carbon compounds such as 1130a and acids such as HCl and HFduring the heating of 141b, such as occurs when a liquid mixturecomprising 141b, 130a, and, optionally, 140a is heated in a distillationcolumn to separate low boiling compounds such as 141b from higherboiling compounds such as 130a (and 140a, if present).

When added to a distillation column, the inhibitor should be added tothe bottom or reboiler section of the column where the temperature ishighest, typically on the order of from about 75 F. to about 200 F.(preferably about 90-160 F.). The temperature at the top of the columnis typically about 20 degrees lower than that at the bottom. Adding theinhibitor to the feed stream to the column, as opposed to the columnbottom, has been found to be ineffective.

The inhibitor is generally fed to the column at a rate sufficient tomaintain a level of inhibitor in the bottoms stream exiting the columnof from about 500 to about 5000 ppm, more typically from about 1500 toabout 3500 ppm.

This embodiment is illustrated in Examples 1-5 below (where percents areweight percent unless otherwise noted). Examples 1-3 employ aconventional carbon steel column.

In a second embodiment it has now been found that the use of nickelalloys such as Nickel, Monel, Inconel, Hastelloy, or Carpenter 20 forthe vessel in which the heating or distillation is conducted iseffective to inhibit the formation of acids and 1130a without the use ofinhibitors. Inconel and Hastelloy alloys are particularly preferred.Exclusion of air from such processes also assists in the inhibition.This embodiment is illustrated by Example 5 and 6.

EXAMPLE 1

A crude, photochlorinated mixture, produced according to the methods ofthe Brooks et al. patent and containing about 100 ppm of 1130a and, asthe other major components, about 98% 141b, 1.5% 140a, and 0.3% 130a,was distilled in a steam-heated column which was operated at atemperature at the column top of about 120 F., a temperature at thecolumn bottom of about 140 F., and a pressure of about 15 PSIG. The 141btaken overhead typically showed the formation of 300 to 600 ppm of 1130aand over 20 ppm acidity (calculated as HCl).

EXAMPLE 2

Example 1 was repeated except that butylene oxide was fed to reboilersection of the column at a rate sufficient to maintain a level of 2500ppm of the butylene oxide in the bottoms stream. There was no detectableformation of 1130a or acid as a result of the distillation.

EXAMPLE 3

Examples 1 and 2 were repeated except that the 140a level in thefeedstream was reduced to about 50 ppm. Distillation as in Example 1resulted in the formation of about 170 ppm of 1130a and over 10 ppmacidity. With the use of butylene oxide as in Example 2, distillationresulted in the formation of only about 30 ppm of 1130 and about 1 ppmof acidity.

EXAMPLE 4

A) A mixture containing as major components about 84.1% 141b, 0.2% 130a,and 15.3% 140a was tested to compare the ability of various inhibitorsto prevent the formation of acidity (the starting mixture contained 5.3ppm acid as HCl). Samples containing 2000 ppm of inhibitor (except inthe control with no inhibitor) were, placed in glass bottles and set oneinch from a 450-watt UV lamp for 5 hours. With no inhibitor (thecontrol) over 120 ppm of acidity resulted. With six inhibitors of thisinvention (DEHA, APO, HO, BO, AMS, and DL) less than 10 ppm of acidityresulted.

B) The above test was repeated except that the samples were placed inmild steel cylinders and heated at 100 degrees Centigrade for 7 hours.With no inhibitor (the control) over 170 ppm of acidity resulted. With10 nine inhibitors of this invention (DEHA, APO, HO, BO, AMS, DL,benzoquinone, 4-methoxyphenol, and 2,6-di-t-butyl-4-methylphenol) lessthan 10 ppm of acidity again resulted.

EXAMPLE 5

Crude, 141b-containing, column bottom material was heated in cylindersmade of different metals and analyzed. A 316 Stainless Steel containerheated to 180 F. for 16.5 hours showed a 5-fold increase in 1130a, whilethe same container heated to 252 F. for 23 hours showed no increase in1130a when 1800 ppm of butylene oxide inhibitor was added. Mild steelcontainers heated to 257 F. for 4 hours showed a 340 ppm increase in1130a with no inhibitor, but only a 50 ppm increase in 1130a when 1600ppm of butylene oxide inhibitor was added. When Monel (an alloycontaining 63-70% by weight nickel) was heated to 257 F. for 4 hours, noincrease in 1130a occurred even though no inhibitor was present.

EXAMPLE 6

Relatively pure 141b samples (99.3% 141b) without inhibitor were placedin glass tubes containing small coupons of various metals and heated for2 hours at 356 F. The mild and stainless steels resulted in theformation of 495-1755 ppm of 1130a, while Inconel 600 (an alloycontaining 72% nickel) and Hastelloy C-276 (an alloy containing about60% nickel) resulted in no 1130a formation, Nickel (99-100% nickel)resulted in 250 ppm of 1130a, Monel 400 (63-70% nickel) resulting in 335ppm of 1130a, and Carpenter 20 (an alloy containing 32-38% nickel)resulted in 450 ppm of 1130a.

What is claimed is:
 1. A method for inhibiting the formation ofvinylidene chloride during the heating or distilling of1,1-dichloro-1-fluoroethane, which method comprises heating ordistilling 1,1-dichloro-1-fluoroethane in a distillation column made ofa nickel alloy.
 2. A method as in claim 1 wherein the alloy is Inconel600.
 3. In a process for separating 1,1-dichloro-1-fluoroethane from aliquid mixture containing 1,1,1,2-tetrachloroethane in a distillationcolumn wherein the 1,1-dichloro-1-fluoroethane comes off as an overheadproduct and the 1,1,1,2-tetrachloroethane comes off as a bottomsproduct, the improvement which consists essentially of feeding saidliquid mixture through a distillation column made of a nickel alloy soas to inhibit formation of vinylidene chloride during the separationprocess.
 4. A process as in claim 3 wherein the alloy is Inconel 600.